in-package name => package
Arguments and Values:
name---a string designator; not evaluated.
package---the package named by name.
Causes the the package named by name to become the current package---that is, the value of *package*. If no such package already exists, an error of type package-error is signaled.
Everything in-package does is also performed at compile time if the call appears as a top level form.
The variable *package* is assigned. If the in-package form is a top level form, this assignment also occurs at compile time.
Affected By: None.
An error of type package-error is signaled if the specified package does not exist.